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28 January 2005 Optical limiting behavior of 4 (2'- hydroxy- naphthyl azo) antipyrine (H-NAP) and its rare-earth complexes
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We report the optical limiting performances of a newly synthesized chromophore, 4 (2'-hydroxy- naphthyl azo ) antipyrine ( H-NAP ) and it's rare earth perchlorate complexes, La ( NAP )2 ClO4 and Dy ( NAP)2 ClO4, in solution for 20ns pulses of wavelength 532nm. Comparing with the limiting response of C60 in toluene (already reported optical limiter), the limiting threshold of H-NAP and it's complexes were found to be much lower. The origin of the optical limiting behavior observed for the samples are under investigation. To elucidate the various phenomena involved, z-scan experiments were performed in all the samples. From the closed aperture data, a negative refractive non-linearity (de-focusing effect) can be inferred in all the three cases. Larger magnitude of n2 is expected to result in a more effective optical limiting, which implies a lower threshold for limiting and correspondingly lower output above threshold. The second hyperpolarizability of the compounds has a negative sign and is much larger than the reported values for fullerenes. The limiting in H-NAP can be attributed to the large nonlinear absorption of the material and in La (NAP)2ClO4 and Dy (NAP)2 ClO4, the main mechanism may be de-focusing caused by the nonlinear refractive index. H-NAP and its rare earth perchlorate complexes can hence be considered as very promising materials for optical power limiting.
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S. Kumari Geetha, C.I. Muneera, and K. S. Bindra "Optical limiting behavior of 4 (2'- hydroxy- naphthyl azo) antipyrine (H-NAP) and its rare-earth complexes", Proc. SPIE 5646, Nonlinear Optical Phenomena and Applications, (28 January 2005);

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